1. Field of the invention
The present invention relates to a hydraulic control valve with a regeneration function for heavy equipment such as an excavator, and more specifically, to a hydraulic control valve capable of maintaining the pressure in a regeneration passage, irrespective of changes in the discharge flow rate of a hydraulic pump, the location of a working device, working speed, a regeneration flow rate and a return flow rate.
2. Description of the Prior Art
In hydraulic circuits, a regeneration function supplies a hydraulic fluid which is returned to a hydraulic tank from a return side of an actuator (e.g. hydraulic cylinder), to a supply side flow path of the actuator by a regeneration valve, thereby ensuring working speed and thus improving the energy efficiency. In addition, it is possible to prevent a cavitation phenomenon from being generated due to short flow rate occurring at the supply side by increased driving speed of the actuator. Therefore, the regeneration function can prolong a lifespan of the respective components and reduce complaint of clients against the hydraulic circuit.
FIGS. 1 to 3 show the construction of a conventional hydraulic control valve for heavy equipment. The following will now describe the operation of the hydraulic control valve.
A hydraulic fluid discharged from a variable displacement hydraulic pump 1 is fed to a check valve C via a supply line 2, and thus the check valve C is pushed upward. As a result, the hydraulic fluid is fed to a supply passage 6 formed in the valve body 3. AS a pilot signal pressure Pi is fed from the exterior, a spool 7 is shifted to a left or right direction to supply the hydraulic fluid which is fed to the supply passage 6 to a first port 4 or a second port 5.
Since the first port 4 is connected to a large chamber 8a of a hydraulic cylinder 8 and the second port 5 is connected to a small chamber 8b, the hydraulic fluid is fed to the large chamber 8a from the supply passage 6 through the first port 4 when the spool 7 is shifted to a right direction. Thus, since the hydraulic cylinder 8 is extended, the hydraulic fluid discharged from the small chamber 8b passes through the second port 5, and is then returned to a hydraulic tank T.
If the spool 7 is shifted in a left direction, the hydraulic fluid is fed to the small chamber 8b from the hydraulic pump 1 via the supply passage 6 and the second port 5. The hydraulic fluid which is discharged from the large chamber 8a by the retraction of the hydraulic cylinder 8 passes through the first port 4, and is then returned to the hydraulic tank T.
In this instance, when the hydraulic cylinder is extended, a part of the hydraulic fluid discharged from the small chamber 8b is fed to the supply passage 6 by a regeneration valve 12, and thus a part of the hydraulic fluid returned to the hydraulic tank T is fed to the supply side of the hydraulic cylinder 8, thereby improving the energy efficiency. In addition, it is possible to prevent the cavitation phenomenon from being generated due to shortage of the hydraulic fluid fed to the hydraulic cylinder 8.
As shown in FIGS. 2 and 3, if the spool 7 is shifted in a right direction, that is, the hydraulic cylinder 8 is extended, the hydraulic fluid discharged from the small chamber 8b passes through the second port 5, and is thus fed to a tank passage 10b via the first regeneration passage 13, the passage 14 and the return passage 16 in order.
As a cross section of the return passage 16 is small to have a small diameter of a hole, the pressure is generated in the first regeneration passage 13. If the pressure is relatively higher than the pressure of the second regeneration passage 15 which is formed in the spool 7, the poppet 17 formed in the spool 7 is moved in a right direction, and thus the hydraulic fluid is fed to the supply passage 6 from the first regeneration passage 13 via the second regeneration passage 15. That is, a part of the hydraulic fluid to be returned to the hydraulic tank T is supplementarily supplied to the supply side.
Meanwhile, in case where strong force is required for operation of the hydraulic cylinder 8, that is, a heavy load is produced, the hydraulic cylinder 8 generates strong force, as the pressure of the first port 4 is under the same condition and back pressure of the second port 5 is weak (i.e. back pressure of the first regeneration passage 13 is weak).
More specifically, if the pressure of the supply passage 6 is above a set value, as shown in FIG. 3, a regeneration spool 22 is moved in a right direction by a piston 21 urged by the pressure of the supply passage 6. As a result, as an opening rate of the return passage 16 is gradually increased, that is, a passing area of the hydraulic fluid is changed, the back pressure of the first regeneration passage 13 is decreased, so that the hydraulic cylinder 8 produces the strong force.
The regeneration spool 22 varying the opening rate of the return passage 16 is resiliently supported by a first resilient member 23 (e.g helical compressive spring), and the piston 21 moved by the pressure of the supply passage 6 comes in close contact with the front of the regeneration spool 22.
If the pressure of the supply passage 6 is increased more than the set pressure, the piston 21 is urged in a right direction, and thus the regeneration spool 22 is also moved in a right direction. Therefore, since the opening rate of the return passage 16 is gradually increased, the pressure of the first regeneration passage 13 is decreased, so that the hydraulic cylinder 8 produces the strong force.
The change of pressure in the first regeneration passage 13, the flow rate passing through the first regeneration passage 13 and the tank passage 10b, and the area of the return passage 16 satisfy the following equation:ΔP=C×(Q/A)2 
ΔP is the change of pressure in the first regeneration passage 13;
C is flow coefficient;
Q is a flow rate moved from the first regeneration passage 13 to the tank passage 10b; and
A is a variable area of the return passage 16.
Here, the flow rate Q may be varied depending upon the supply flow rate of the hydraulic pump 1, the position of the working devices, and the flow rate regenerated through the second regeneration passage 15.
The pressure of the first regeneration passage 13 is varied in accordance with the change of the flow rate Q and the area A, and the pressure of the supply passage 6 is varied in line with the fluctuation of the regeneration passage. Thus, the regeneration spool 22 urged by the first resilient member 23 is moved by the regeneration spool 22.
The fluctuation of the pressures in the first and second ports 4 and 5 causes the hydraulic cylinder 8 to unnaturally drive, that is, hunting happens due to irregular drive. Therefore, it is difficult to control the driving of the hydraulic cylinder 8.
As shown in FIG. 3, in case where the regeneration valve 12 is assembled to or disassembled from the valve body 3, it is not possible to assemble or disassemble the valve body 3 engaged with the regeneration valve 12.
In case where the valve body 3 engaged with the regeneration valve 12 in a separation type is disassembled, the disassembling workability is lowered since some parts of the regeneration valve 12 are held in the engaged portion of the valve body 3.
Besides, if a component is dropped through carelessness at disassembly of the regeneration valve 12, the component is lost, or the component is contaminated by dirt or soil. The contamination of the component causes additional washing to be performed on the component, thereby lowering the work efficiency.
As shown in FIG. 3, according to the application of inner drain manner in which the hydraulic fluid is drained from a back-pressure chamber 24 through a drain hole 12a, there is a problem in that the fluctuation of the back pressure causes the hunting, since the back pressure of the hydraulic tank is directly connected in the equipment.